Two men were arrested over the murder of Mary-Ann Leneghan last night as police continued to question a third man in his 20s.
The arrests came as a bedsit above a massage parlour in a red-light district of Reading was searched by Thames Valley police.
The 16-year-old and a friend, aged 18, were abducted by a gang of men who physically and sexually assaulted them before dumping them in a park. Mary-Ann died after being stabbed in the neck but her friend survived, despite being shot in the head.
Police confirmed that they are investigating possible links between the assaults and an arson attack on the 18-year-old's house two weeks before. A firebomb damaged the girl's front door and is subject to an ongoing investigation.
A friend of Mary-Ann's said yesterday that the 16-year-old had gone missing for about a month after she "got in with the wrong crowd", it was reported.
Police confirmed that a third girl was with the teenagers shortly before they were snatched from a car park in Reading late on Friday night.
The investigation moved yesterday to a flat in the Oxford Road area of Reading, a red-light district. The property was raided at 10pm the previous night. Forensic specialists are searching the property.
A local woman said she saw Mary-Ann and her friend on a corner near the property late at night and in the early hours.
She said: "I always used to see Mary-Ann hanging around in odd places. She used to be on the Oxford Road at odd times - first thing in the morning or last thing at night - with gangs of people." The woman added that she had spotted her and her friend "every other week" on Oxford Road for the past six months.
Mary-Ann and her friend were taken to a guest house where they were sexually assaulted and tortured in an ordeal that lasted three hours. The two teenagers were then dumped in Prospect Park on Saturday morning. The 18-year-old is recovering in hospital.
Earlier in the evening, the two friends had been in a car with a third girl in the car park of the Wallingford Arms pub before the attack.
The police said: "This [third] girl was in no way involved in the incident."
Police are continuing to question a man in his 20s, who was arrested in south London and is considered a strong suspect.
Detective Superintendent Mark Warwick, who is leading the investigation, said: "This crime is one of the most horrendous I have seen. It has shocked and stunned all officers who have been involved.
"We find this offence as difficult to comprehend as the residents of Reading and our sincerest and deepest sympathies remain with the family and friends of the two girls involved.
"An incident of this nature is bound to send shockwaves in the community and, with that, comes speculation, rumour and gossip. Everyone has their own opinion of what happened... We are just as keen to get to the bottom of what happened... as everyone else."