chief, key, main, number-one, primary (AmE), prime
She has been identified as the chief suspect.

likely, logical (AmE), obvious, possible, potential
usual
criminal, murder, terror, terrorism (esp. AmE), terrorist

have, identify (sb as), name (sb as)
The police have several suspects.

apprehend, arrest, capture, catch, detain, hold, round up
The army rounded up all the usual suspects.

interrogate, interview, question
charge
release
extradite, hand over

suspect for
The letter makes him a possible suspect for her murder.

suspect in
Two men were arrested as suspects in the bombing.

be, look, seem
render sth
The theory is rendered suspect by its reliance on now discredited sources.

extremely, fairly, very, etc.
deeply, highly
Some of the evidence was deeply suspect.

increasingly
a little, slightly, etc.
inherently
constitutionally (esp. AmE), morally, politically
the forced adoption of children of politically suspect citizens

Suspect is used with these nouns:
package