I've went to the safehouse, killed the Courser there, but the marker still points to the dead Courser.

I've tried selecting him with the console open, then typing resurrect, but it didn't worked.

Any ideas ? Thanks.

http://fallout.wikia.com/wiki/Operation_Ticonderoga

Scroll down to bugs.

This can be fixed by entering the following in console: setstage RR301 XXX

Where XXX is the stage number found below:

Thanks.

I set the stage to report back to Desdemona and it worked.