Purity: Confidence vs. Doubt in Funeral Duties
Practical Laws of Islam as per the teachings of Ayatullah Sistani
Ruling 532:
If a person is confident that others are engaged in attending to the duties relating to a deceased person, it is not obligatory for him to start doing those things. However, if one doubts or merely supposes [that others are engaged in attending to those duties], he must start doing them.
-Ayatullah Sistani, Practical Laws of Islam, Purification (Taharah)