Here is a video of him giving a speech at a Fatah rally, and here is a video he uploaded showing him posing with weapons as well as a photo (that is probably Photoshopped) of him with Arafat.
He is part of the Mohammed Dahlan-leaning faction of Fatah in Gaza.
On July 28, Hamas security placed Lashin under "house arrest" - and shot him in the legs in order to keep him in his house.
We know Hamas has shot some suspected "collaborators" in the legs for their "house arrest." But Lashin does not appear to be a collaborator, he has extensive anti-Israel material on his Facebook page yet is not pro-Hamas.
One of his Fatah friends expressed frustration that Hamas and Islamic Jihad were not including Fatah in their strategy sessions during the war, even though Fatah has taken credit for hundreds of rockets towards Israel.
Hamas used the war as cover to go after its political enemies. Knowing that Israel would give warnings to people to leave their houses, they used the excuse of "house arrest" and collaboration to enforce their desire to keep Fatah members in their houses, to be killed. This way they achieve two goals: indirectly killing their enemies and being able to blame Israel for killing Gazans who were unable to leave their homes!
The Western media is utterly silent about the level of depravity of Hamas in Gaza.