AMSTERDAM, Netherlands -- A five-page letter pinned to the body of a Dutch filmmaker brutally murdered after making a movie critical of Islam called for Muslims to rise up against the "infidel enemies" in the West.

Other messages -- later left at the sidewalk shrine where Theo van Gogh's throat was slashed -- dripped with equal venom against radical Islam. "Enemies live among us," read one missive in a bed of flowers, votive candles and crosses.

Europe's complex interplay with Islam appears to stand at a tipping point and Tuesday's slaying of the 47-year-old filmmaker as he was riding his bike down a busy Amsterdam boulevard could indicate one direction in which it is headed.

"The Muslims say they're scared," said mourner Nicolette Toering. "No, we're scared."

Dutch authorities were investigating whether the chief suspect in the slaying, a 26-year-old Dutch-Moroccan man arrested shortly after the attack on terrorism-related charges, acted alone out of rage or had links to wider extremist networks. Police have detained several other suspects facing charges including conspiracy to murder.

The letter stuck to the victim's body threatened death to Somali-born lawmaker Ayaan Hirsi Ali, who scripted van Gogh's last film, "Submission," which criticized the treatment of women under Islam.

It also predicted the downfall of the "infidel enemies of Islam" in Europe, America and the Netherlands.

Facing hard choices

Heightening fears nationwide, two Dutch men were arrested late Friday for allegedly posting a video on the Internet calling for the beheading of right-wing lawmaker Geert Wilders for perceived insults to Islam.

The attack and threats have underscored the hard political and social choices that European leaders face about Muslims and the wider Islamic world.

In December, European Union leaders will decide whether to overlook widespread public objections and move ahead with membership talks with Turkey, a Muslim nation of about 70 million people and a galloping birthrate that could push it past Germany's population in a generation.

"Right now the West sees all Islam as a kind of monolith and wipes away all nuances," said Akbar Ahmed, a professor of Islamic studies at American University in Washington and a former Pakistani ambassador to Britain.

"What is really happening is a struggle within Islam itself in the West. Some want to draw boundaries around Islam in Europe. Other Muslims want to deal with non-Muslims in a broad and tolerant way. It's not new to Islam. It's just new to Europe."