The 39-year-old man was arrested after three girls aged 10 to 12 reported that he pulled down his trousers, exposed his genitals and began pleasuring himself in front of them, the 20 Minuten newspaper reported.
The frightened girls got off the tram at the next stop and alerted authorities about the incident, which occurred on May 21st, the newspaper said.
A few days earlier, 14-year-old boys spotted the culprit masturbating in public in a Zurich park, according to court evidence.
The boys used a mobile phone to film the man and later gave a recording to police.
He was ultimately arrested after he masturbated several times in front of students at a secondary school park in the city.
The perpetrator told the court he was acting to “release tensions”.
The judge in case said the man had acted in a flagrantly “unabashed” manner, convicting him of multiple sexual acts with children, in addition to exhibitionism offences, 20 Minuten said.
The court sentenced him to a suspended six-month jail sentence, fined him 1,800 francs and ordered him to receive pyschotherapy counselling for three years “as a last chance”, the newspaper reported.