On Monday police said they strongly suspected that 23-year-old Tobias Kuster was involved in the murder on June 30th.

The suspect, a prisoner incarcerated in Pöschwies prison, had failed to return from day release on June 23rd and was still at large at the time of the killing.

In prison since February 2014 for violent crimes – but not murder – Kuster is classified as violent and “likely to be armed,” said police.

He was due to be released on good behaviour at the end of 2017,

“Up until now, Tobias Kuster, who is strongly suspected to be connected to the crime, could not be found,” police said in a statement on Wednesday.

A reward of 10,000 francs is now offered “for evidence which leads to the clarification of the crime”.

Anyone with information is asked to call Zurich cantonal police on 044 247 2211.

Rewards are rarely offered in Switzerland, but there have been a few high profile cases of late.

Last year a 10,000 franc reward was offered in the case of a violent rape in Emmen, near Lucerne, which left its victim paralyzed.

The rapist has not yet been found.

And in February this year police posted a 100,000 franc reward – one of the largest ever – in the case of a savage quadruple murder in the village of Rupperswil in December 2015.

The killer – a local man – was finally caught in May but without information gained by offering the reward.

The money was instead given to the police investigators who solved the case.