A teenager who has been charged of throwing a six-year-old French boy from the viewing platform at Tate Modern may have spent up to two hours selecting his victim, Scotland Yard has said.The 17-year-old, who has been charged on suspicion of attempted murder, is thought to have been hanging around the gallery acting suspiciously from around midday on Sunday.At some point he ascended to the 10th floor viewing level and just after 2.30pm allegedly grabbed a six-year-old boy, who was with his mother, and hurled him over the balcony.The youngster, a French national, who was visiting London with his family, remained in a critical but stable condition in hospital.The boy fell five storeys, around 100ft, before landing on a fifth floor roof of the gallery.Witnesses described hearing a loud bang before seeing a woman screaming: “Where’s my son, where’s my son?.”The little boy was airlifted to hospital, where it was initially feared that he might not survive. The Tate Modern is one of London’s most popular attractions The viewing platform has been closed since the incident But in a statement issued on Monday, the Metropolitan Police said, while he remained in a critical condition, he was no longer in a “life threatening situation”.Detectives said they had not been able to establish a motive for the “truly shocking” incident, but eyewitnesses at the scene, claimed the suspect had shouted that social services were to blame for his actions. “We are grateful for the support of the public, some of whom detained the male arrested in the immediate aftermath of the incident. He was arrested by officers very quickly afterward.”This was a truly shocking incident, and people will understandably be searching for answers.”At the moment, this is being treated as an isolated event with no distinct or apparent motive. There is no link between the victim and male arrested.”It would have been incredibly distressing to watch, and it may be that you left Tate Modern very quickly after. If you have not yet spoken to us about what you saw, please contact us without delay.”My team is also very keen to talk to you if you witnessed a male whose behaviour seemed out of place, suspicious or worrying, in the hour or two before the incident in or near the gallery. It may be that this is something which has only just come back to you. If so, please still make that call to the investigation team.” The boy was described as being in a stable condition Police are appealing for witnesses for the incident to come forward The teenager was spotted standing calmly near the scene surrounded by a group of people, who looked to be in complete shock.Security guards at the south bank gallery then took the suspect into the cafe, apparently mistaking him for a member of the boys family. It was only when eyewitnesses pointed out that he was the alleged culprit that the boy was seized by members of the public.Witnesses said an angry bystander attacked the youth and punched him in the face, before members of the public locked him in a lavatory for his own protection.Thousands of people were at the attraction on Sunday afternoon and detectives have asked for anyone who was spotted a young man acting in a “suspicious or worrying” manner in the two hours running up to the incident to contact them.One witness also told the Telegraph that she and her family had been followed in the gallery by an unkempt man who had been taking photographs of the children.She described the suspect as white, with scraggly hair and a beard. Sunday’s incident did not appear to deter guests, with a steady flow of people entering the art gallery throughout the day. Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings. On Monday the Tate remained open to the public but notices alerted the public to the fact the viewing gallery was closed.The restaurant on the ninth storey also remained closed and the stairway leading up to the floor above was cordoned off and manned by security staff. Detective Chief Inspector John Massey said: “We are providing around the clock support to the little boy’s family as they wait for more news on his condition and our priority remains to determine what led to [Sunday’s] events.