Chris Brown is being investigated for attempted murder in connection with his alleged attack on Rihanna.

The Run It singer was originally arrested on suspicion of making criminal threats after the February 8 altercation that left his ex-girlfriend with contusions to her forehead, a bloody noise and a split lip.

Now it's emerged that the singer is being investigated for a variety of felonies, including domestic violence, assault resulting in great bodily injury and attempted murder.

The attempted murder probe is based on claims Rihanna made to police that Chris said, "I'm going to kill you," as he had his hands around her neck.

But, according to E! News - who cite sources close to the L.A. Police Department's investigation - it will be difficult to make any serious felony charges stick because there are no direct witnesses to the incident other than Rihanna and Chris.

Yesterday Rihanna's shocking injuries were made public when a shocking photograph purportedly taken shortly after the incident was posted online.