The Shin Bet security service and Jerusalem police have yet to locate suspects in the pipe bomb attack against left-wing Hebrew University professor Zeev Sternhell last week.

Sternhell, an Israel Prize laureate and frequent Haaretz contributor, was lightly injured when a pipe bomb exploded outside his home in the capital. Sternhell is a vocal opponent of Israel's military and settlement activities in the West Bank.

In the meantime, the police have decided not to bolster security around prominent left-wing activists in the city due to the absence of intelligence of further attacks being planned.

Shin Bet agents have been combing Internet forums associated with right-wing organizations in recent days for suspicious postings. They are also analyzing an e-mail sent over the weekend to media outlets and Knesset members in which the sender exposes the identity of a 17-year-old youth who, he claims, committed the attack.

The anonymous author attached screen captures to the message purporting to show the assailant's postings to the forum "Hayamin" ("The right").

The e-mail also includes an undated posting in which the youth invites other users to join him in attacking a well-known leftist activist. The attack, however, was supposed to have taken place the day after Sternhell was targeted.

"On September 25, 2008, we the members of the true rightist organization will embark on a revenge mission on a senior leftist political figure. Whoever is interested in joining is asked to send me a message privately, not through the forum," it said.

Another e-mail indicated the sender's desire to "shut up" MK Zahava Gal-On and Prime Minister Ehud Olmert with an army-issue weapon.

The police said the content of the messages is being examined.

"From the moment I returned from the hospital my life has gone on exactly as it has before. I'll lock the door every evening against burglars, I'll continue to write what I always have, and preach what I preach," Sternhell said from his home Friday after returning from the hospital.

"If a simple citizen like me can't express his opinion, that means we're approaching the end of the road for democracy."