I think where it all leads concerning Quinn's thoughts on Dexter add up well enough; he still felt uneasy about him, but after the Stan Liddy business and his feelings for Debra there wasn't much to do about it.

Than the sketch of Kyle Butler

Pretty long history at that point between Dexter and Quinn , going back to Dexter witnessing Quinn take the money. At that point Quinn tried to buddy up with Dexter and the cold shoulder from Dexter gave Quinn some ideas. Than seeing Dexter go to the club that night and sneak off when spotted , the constant leaving work and the physical alertacatio. In the parking lot. Alll were very small issues but than the 911 call mixed with no emotions at the crime scene.

if there's only one thing that pisses you off about this show, you're lucky

I hated Quinn! I didn't get why Batista respected him so much & encouraged him. He was a dirty cop and not a great detective either.

Doakes made sense that he was able to see something wrong with Dexter. Quinn, I never bought though. First he never really seemed that good of a detective. Pretty much nothing he ever did turned out right. He made the wrong calls and was on the wrong track constantly. If he was supposed to be able to tell there was something about Dexter, yet couldn't see the problems of the guy he allied himself with to see he was trouble. And so far as being able to see there was something wrong with Dexter, well that doesn't fit with him trying to buddy up to Dexter when he knew Dexter saw him. It was only after Dexter didn't want to be his buddy that he decides there's something wrong with him. He seemed like he had been turned down by a girl for a date after that. He really seemed like the guy that hit on a girl, she rejected him, it pisses him off and suddenly he's bad mouthing her, saying she's the crazy one, and he never wanted to be with her to begin with while he's stalking her at the same time.
To Love and win is the best thing. To Love and lose, the next best.

If you're referring to Quinn's thoughts while listening to Dexter's 911 recording in Season 5, I completely agree. He had suspicions before, but I think at that point it really builds up.

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