Investigators are looking for clues into the motive which led James Holmes to carry out an attack and allegedly kill 12 people at the screening of the new Batman film on Thursday night.
Bomb disposal experts have started the delicate process of entering Holmes' flat in Denver, Colorado, and have warned the intricate wiring means they may have to remove trip wiring which could cause explosives.
The 24-year-old is said to have allegedly created a 'sophisticated' and potentially deadly trip wiring explosive at his home.
Police described the scene as something they have never experienced before and have been using robots to enter the property.
Detectives are also investigating a profile believed to have been set up by the University dropout on a sex-cruising website.
The AdultFriendFinder page, which belongs to a 24-year-old user calling himself 'ClassicJimbo', features pictures of a man who is remarkably similar to Holmes but with dyed red hair.
The profile said he is looking for 'casual sex' or a 'fling' - and writes, 'Will you visit me in prison?'
While there are a couple of minor discrepancies on the profile, including a birth date and height which are slightly different to those reported by officials, it is convincing enough to have attracted the attention of police, according to Mediaite.
The man's red hair fits with the statement by NYPD boss Ray Kelly that the gunman had dyed his hair before the cinema attack.
The user, who admits to not being well-endowed, writes: 'Looking for a fling or casual sex gal. Am a nice guy. Well, as nice enough of a guy who does these sort of shenanigans.'
Under 'Education', he writes, 'Some grad school' - which would fit with an identification of him as PhD dropout Holmes.
'ClassicJimbo' created his account on July 5, and last accessed it on Tuesday.
Holmes, who referred to himself as 'The Joker', was equipped with an arsenal of more than 6,000 rounds of ammunition when he allegedly killed or injured 70 cinema-goers at a screening of The Dark Knight Rises.
Six of the victims who had been named by the end of the night were Jessica Ghawi, 24, Alex Sullivan, 27, John Thomas Larimer, 27, Matt McQuinn, 26, Micayla Medek, 23, and AJ Boik, 18.
Holmes had bought a movie ticket and sat down before sneaking out before the first fight scene in the film. He is believed to have propped open a fire exit before driving his car back to the door.
Inside the boot of his car he had an AR-15 assault rifle, a Remington 870 shotgun, and two Glock handguns. Now armed with the weapons he burst back into theatre 16 and opened fire shortly before 12.30am.
Some witnesses said they first thought the shooting was part of the movie and said Holmes moved up the cinema aisle, shooting anyone who tried to flee.
Detectives said Holmes was dressed all in black, wearing a ballistic helmet, a tactical ballistic vest, ballistic leggings, a throat protector, a groin protector, a gas mask and black tactical gloves.
New York Police Commissioner Ray Kelly said: 'It clearly looks like a deranged individual. He had his hair painted red. He said he was "The Joker", obviously the enemy of Batman.'
The Joker is the arch villain in Batman but Holmes' black outfit, gas mask and multiple weapons bears similarities to Bane, the badman in the new Batman film. Bane also wires Gotham City with explosives
Detectives said they have ruled out all links to terrorism but reported that Holmes' living room had what looked like sophisticated trip wires connected to bottles containing unknown liquid.
Bomb disposal experts evacuated neighbours in five nearby buildings and said it could take time to work through the intricate wiring.
Student Kaitlyn Fonzi, 20, and boyfriend nurse Chris Rodriguez, 30, said they fear Holmes may have tried to lure them into his booby trapped apartment.
The pair lived below Holmes and said they heard loud techno music playing at 12am - moments before the shooting spree started.
Music blared from the flat for an hour and Kaitlyn said: 'I went upstairs to complain but there was no one there. The door wasn't locked and I was going to poke my head in but chickened out.
'I'm glad I didn't. We think the music was on a timer.'
A neighbour also reported that police, who were searching Holmes' apartment for explosives, asked him if he had seen 'a white guy with crazy hair, possibly dyed unnatural colors', the Denver Post said.
Police said they arrested Holmes in a car park behind the cinema.
With some of the deceased still missing, authorities have said they will not release a full list of those who were killed or injured in the attack.
However, families who have been informed of the deaths have chosen to come forward to pay tribute to their loved ones.
Alex Sullivan said he had 'planned a weekend of fun' and had started with celebrating his birthday 27th birthday by watching the screening with friends.
He was also looking forward to celebrating his first wedding anniversary on Sunday. Late on Friday, Sullivan's family confirmed that police told them he was among those killed.
Micayla Medek, 23, was also among the dead, her father's cousin, Anita Busch, confirmed the death.
The family of Navy serviceman John Thomas Larimer, 27, said they anxiously tried to contact him but realised he was among the dead when a Navy notification team contacted them.
The knew he had been at the theatre and later said: 'At this point, our other son Noel is in Denver working with the Navy and the family here in Illinois to make arrangements to bring John home.
Eighteen-year-old AJ Boik died after traveling to the midnight viewing with his friend Jordan Crofter, 19, who is believed to be distraught over the death.
Matt McQuinn, 26, has been hailed a hero after diving in front of his girlfriend Samantha Yowler as Holmes took aim.
The death of Jessica Ghawi, who was also known as Jessica Redfield, was a 'complete and utter shock,' said her brother, Jordan Ghawi.
The 24-year-old only last month wrote about how she had survived a shooting at the Eaton Centre mall in Toronto which killed two people and left several injured.
She had moved to Denver from Texas about a year ago to pursue her dreams of becoming a TV sports presenter.
It has also emerged that Holmes, who is accused of killing 12 and injuring 58 had been studying at the University of Colorado's medical campus until June this year.
The massacre took place 20 miles from Columbine High School where two students killed 13 people in 1999.
On Friday night, well over 1,000 people joined vigils at nearby churches and outside the theatre itself to commemorate the victims of the shooting.
Families of the dead paid tribute to their loved ones after receiving news that the worst had indeed come to pass.
Alex Sullivan's uncle said: 'He was a very, very good young man. He always had a smile, always made you laugh. He had a little bit of comic in him. Witty, smart. He was loving, had a big heart.'
The cousin of Micayla Medek said that the report of her death had come almost as a relief after a terrible day of waiting for news.
'I hope this evil act doesn't shake people's faith in God,' she added.
Holmes's firepower included 3,000 rounds of ammunition for his A-15 assault rifle including a 100 drum magazine which could have fired a staggering 60 rounds a minute.
Chillingly, he bought it all over the internet with no apparent checks to see if he was stockpiling.
The full scale of his planning was revealed by Aurora police chief Dan Oates in an emotional press conference in which he almost broke down in tears and vowed to ensure Holmes went to jail.
He said: 'The most important thing is that there is justice for these victims, and that justice will occur in a courtroom'.
Chief Oates said that Holmes had stocked up in just 60 days before going on his killing spree.
He said: 'He purchased four guns at local gun shops and through the Internet he purchased over 6,000 rounds of ammunition, more than 3,000 rounds of 223 ammunition for the assault rifle, 3,000 rounds of 40 caliber ammunition for the two glocks in his possession, 300 rounds for the 12 gauge shotgun.
'Also through the internet he purchased multiple magazines for the 223 caliber assault rifle including one 100 round drum magazine which was recovered from the scene.'
'Even if it was semi-automatic I'm told by experts that with that drum magazine he could have got off 50 to 60 rounds within a minute. As far as we know it was a pretty rapid pace of fire in the theatre.
'My understanding is that all the weapons he possessed he possessed legally and all the clips that he possessed he possessed legally and all the ammunition he possessed, he possessed legally.'
A source familiar with the investigation told the Daily Mail: 'It's insane that he was able to buy all this stuff so easily and legally.
'He had an arsenal and nobody stopped him. With Columbine on everyone's minds it makes you wonder how much has really changed'.
When asked how the investigation had affected him personally, Mr Oates nearly broke down in tears and had to pause to compose himself.
He said: 'Our cops went through a lot. They rushed people out of that theatre into police cars... I've heard some compelling stories...
'One of the things we're working on is how we are going to deal with our own trauma. Somehow in the next couple of days, when this has slowed down, one of our highest priorities is to deal with our own officers'.