Zlepe was killed by a Chelgrian agent when he arrived at the Beidite entity Critoletli. The brief description of his assailant ("—fear and the sudden tearing pain, the huge white-furred face suddenly filling his vision") matches several of Chelgrians we know were involved in the plot, most especially the 'heavy' (Eweirl) that the Estodian brought to the meeting with Quilan during his training. His white fur is mentioned no less than eight times in the book.
The bulky-looking male dressed as a clerk had been about to strike; he
had rocked back on his haunches and his sleeves were rolled back to
reveal tightly muscled arms, though his claws were only half exposed.
There was a radiant, almost feral look on his white-furred face that
lasted for a moment and even brightened for an instant as Quilan
turned to confront him but then he glanced at the Estodien and
relaxed, sitting back and lowering his arms and his head in what might
have been a bow.
Ultimately Zlepe was being very indiscreet (signalling his location multiple tens of days ahead of his arrival) and the fact that a Culture citizen who was unexpectedly close to the Chelgrian's initial weapons test, then trying to get out of the airsphere at high speed would have attracted a lot of attention. Note that the assailant can't have been Ziller(!) as he was on Masaq at the time of the attack.
—Some of the frozen liquid taken from the edges of the wound which the creature suffered upon its neck region has provided biological instruction set information which tends to indicate that the woundinflicting agent may have been an individual of the species known as the Lesser Reviled.
—That is interesting. Their name was earlier the Chelgrians, or the Chel, before the outrage that befell the Sansemin occurred. To what level of completeness was the analysis of the human form which was found to be implicit in the creature that we see before us taken?