Two things have
been clearly stated in the comics.
1. The Chief has acknowledged that he knew Gar's father (the
extent of this was never fully explored).
2. The Chief was responsible for not only the accidents that gave
Robotman, Negative Man, and Elasti-Girl their powers, BUT he was also
behind the accident that destroyed the Brain's body (in Teen Titans
#37, it's revealed that the Brain was intended to be Robotman, but
Mallah fled with the Brain before the Chief could put it in the robot
Now, based on these two facts, there is a minute possiblity that the
Chief was somehow involved in how Gar received his powers.
In Gar's initial origins, he contracted Sakutia as a child. If
the Chief was at the same research station, following this particular
origin, and exposed the young boy to the deadly Sakutia, then guided
the experiments Mark Logan used to save his son's life.
Gar's most recent origin says that he was bitten by a rare green
monkey, which infected him with the Sakutia. It makes for more of
a "stretch," but if the Chief was at the research station at the time,
he could have captured then let loose a green monkey in the vicinity of
two possible victims (either Gar, or his mother, who was outside with
him at the time). Again, the Chief might also have guided Mark
Logan's research in a way that the cure had the lasting effect of
bestowing shapeshifting powers.
Yes, this is simply a theory, but it is based on known facts.
Hopefully some writer will pick up on this and possibly explore the