This took 20 seconds on google.
From the day of his murder:
"2 November 2004
AMSTERDAM — Immigrant groups in the Netherlands have forthrightly condemned the assassination of filmmaker and columnist Theo van Gogh in Amsterdam on Tuesday morning.
The Municipal Moroccan Council (SMR) said the "cowardly murder" must not lead to a worsening of relations between Muslims and other residents in Amsterdam. The SMR also described Van Gogh's murder as "despicable".
The SMR said organisations had to do everything to ensure tensions did not escalate in the city now that it was known the suspected killer has both Dutch and Moroccan nationality.
SMR chairman Abdou Menebhi said he hoped the Moroccan community would not suffer a backlash because of the killing. "Escalation is in nobody's interest," he said.
"We call on all Amsterdammers to keep a cool head to come to terms with this murder in a calm manner and to bid farewell to Van Gogh in a dignified fashion," Menebhi said.
Ayhan Tonca of the Turkish Cultural Federation said no motive could justify the killing and that everyone must condemn it. But he cautioned that the identity of the perpetrator had yet to be properly established.
"
http://www.expatica.com/nl/news/country-news/Muslim-groups-condemn-filmmakers-murder_123473.html
This from a few days after:
"Several thousand people demonstrated on Amsterdam's central Dam square and railway drivers were urged to honk their horns to protest the murder.
People banged on drums, pots and pans and blew whistles for some 15 minutes, with some participants holding up signs saying "Muslims against Violence."
Abdou Menebhi, of the Amsterdam Moroccan council, urged his co-religionists to obey a minute of silence in the mosque in the evening during regular Ramadan holy month prayers.
The UMAH association of Moroccan-Dutch academics said they did not share Van Gogh's opinions but condemned his murder."
Source:
http://www.rense.com/general59/shot.htm
So yes Muslim leaders did and have condemned the murder, as such your claim that they did not is inaccurate.
And yet they did.