Berlin - The man who attacked passengers on a crowded Swiss train with a knife and a burning liquid, died of his wounds on Sunday, as did one of his victims, Swiss police said. Three others remained in critical condition.Police are still searching for a motive, but said there's no indication the suspect, identified only as a 27-year-old Swiss man from a neighbouring region, had ties to extremist groups.The three people in critical condition include a 6-year-old child, and their wounds are considered life-threatening, St Gallen canton (state) police spokesperson Hans-Peter Kruesi told The Associated Press.Swiss police searched the suspect's home after the Saturday afternoon attack on the train as it neared the station in Salez, close to the Liechtenstein border. Kruesi would not comment on what evidence was seized at the home, but said "so far there are no indications this was a terrorist or politically motivated crime".Police were not able to question the suspect before he died, Kruesi said, adding that the man had no criminal record and was not previously known to police.According to a video of the attack evaluated by police, the assailant acted alone, attacking passengers on the train between Buchs and Sennwald with a knife and then a burning liquid, which is now being analysed by a police forensics team.Five passengers on the train were wounded in the attack and a sixth person on the train platform was wounded as he pulled the burning suspect off the train, police said.The Swiss train attack again illustrates how difficult it is for authorities to protect the continent's labyrinthine transport system, particularly against individuals wielding unsophisticated weapons.Last month in neighbouring Germany, a 17-year-old refugee from Afghanistan used an axe and a knife to wound four tourists on a train, and stabbed a woman as he fled. The attacker was shot and killed by police. All his victims survived.In May at a train station in the German state of Bavaria, a 27-year-old German man who had been in psychiatric care stabbed commuters, killing one and wounding three others before being apprehended by police.Last year a heavily armed gunman opened fire on a high-speed Amsterdam to Paris train, but was overpowered by two young American soldiers and their companion.