Human Rights Watch and its reports on Syria

When armed groups are accused of committing massacres, Human Rights Watch (even in communication with me) claims that it will investigate.  I have not yet heard of one conclusive report on massacres or car bombs by armed groups.  In fact, they claim it is not easy to investigate in Syria due to the dangers. But when the government commits a war crimes (as it habitually does), Human Rights Watch finishes its investigation in a matter of days:  "“The extent of the damage from a single strike, the lack of aircraft in the area at the time, and reports of ballistic missiles being launched from a military base near Damascus..."  So if there are "reports" why investigate? Just publish those reports.  But please tell me: what are those reports?