ROME (AP) — The lawyer for the family of an Italian researcher tortured and killed in Egypt urged five key Egyptian suspects on Wednesday to come forward and say what they know, and added that many more people are implicated in the slaying.

Attorney Alessandra Ballerini read out the names Wednesday of the five secret service members and police investigators whom Rome prosecutors have identified as suspects in Giulio Regeni's abduction.

"These people should be afraid" to travel, she said, and added that as many as 20-40 people were actually involved in Regeni's abduction, torture and slaying. "They should have the prudence to know that it's in their interest to speak up first and not last."

Regeni, a 28-year-old Cambridge University graduate student, was researching trade unions in Egypt when he disappeared in Cairo on January 25, 2016 — the fifth anniversary of Egypt's popular uprising. His body was found several days later by the side of a highway near Cairo with torture marks.

Rome prosecutors on Tuesday formally opened an investigation into the five key Egyptian suspects, taking action because of what Ballerini said was more than a year-long delay after Italy presented Egypt with the evidence it had gathered so far.

"We waited in silence for almost a year," said Regeni's father, Claudio.

Italy has been pushing Cairo since the death to identify and prosecute those responsible for torturing and killing Regeni but has increased pressure as the third anniversary of his death approaches.

Italy's lower house of Parliament cut off parliamentary relations over the case, and the Foreign Ministry last week formally summoned the Egyptian ambassador to Rome to prompt Cairo to "act rapidly" on the case, following a recent meeting between Egyptian and Italian prosecutors.