The spear is presumably the murder weapon.

这矛很可能就是凶器。

《柯林斯英汉双解大词典》

Officers combed the woods for the murder weapon.

警官们彻底搜查了那片树林，寻找杀人凶器。

《柯林斯英汉双解大词典》

The police still haven't found the murder weapon.

警方仍未找到谋杀的凶器。

《牛津词典》

This information can show what kind of weapon was used in a murder.

VOA: special.2010.05.05

Officers have found the murder weapon, and an investigation is under way, it reports.

BBC: Police outside a school in Nanping, Fujian (23 March 2010)

It was revealed that the knife was found in Simpson's master bedroom but is not the murder weapon.

CNN: O.J. Simpson trial: Houseguest Kato Kaelin testifies

Question from: lisa: How does the distinct golf club as murder weapon work to solidify the case against Skakel?

CNN: Moxley Case: Chat with first reporter on the scene