The 22-year-old man, named by police as Kris Van Ooijen, fled the Königsfelden psychiatric hospital in Windisch in the canton of Aargau in the early hours of Saturday, cantonal police said in a statement on Saturday.
Police launched a search for the fugitive at 3.30am but admitted they had “no clues about his whereabouts”.
Van Ooijen was convicted in 2013 of killing a 17-year-old Vietnamese girl when he, too, was still a teenager.
After connecting online, the killer and his victim met in person in August 2009 when Van Ooijen battered the girl to death with a piece of wood and hid her body in a forest in Sessa, in the canton of Ticino. It wasn't until June 2010 that the victim's body was found by a hiker.
Convicted by Aargau's youth court, Van Ooijen was judged to have a severe mental disorder and was sentenced to four years in prison before being transferred to a closed psychiatric ward.
He had only recently been transferred to Windisch from a juvenile correctional institute in Uitikon and had refused to be treated, saying he was innocent of the crime, reported 20 Minutes.
According to one witness, Van Ooijen could now be back in Ticino.
Speaking to local news portal Tio on Sunday, the receptionist of a hotel in Locarno said the man may have come looking for a room on Saturday afternoon.
“He spoke German and appeared very strange,” said the receptionist, who refused to give him a room in the hotel.
“Only later did I read the articles about the fugitive from Aargau and I recognized his face,” she said.
Aargau cantonal police told the paper they do not exclude the possibility that the man may be in Ticino, but “have received many reports”.
The situation has angered the family of the victim.
Speaking to Blick, her brother said: “People like this should stay in prison forever. We now see exactly what this therapy for murdering my sister has been good for.”
In a statement, the Königsfelden psychiatric hospital said it was “closely collaborating” with the authorities investigating how the killer could have escaped from the ward.
The hospital stressed its security measures but said the ward “was not designed as a high-security system” and consequently there “remains a risk of a breakout.”
The man used violence to flee, it said.
Anyone with information should tell Aargau cantonal police by calling the 117 emergency number.