[leephillips]

You sure? I wasn’t.

“John regarded Mary suspiciously”

“Sharon suspected her husband of cheating. She looked through his emails suspiciously.”

[tczMUFlmoNk]

It can mean either. "Suspicious behavior" doesn't mean that the behavior thinks that you've done something wrong.

"She's suspicious" can mean either that I suspect her intentions or that she suspects someone else's intentions.