Mary Woods wrote:

Kellermann also used a control case study, limiting his cases to the
following criteria; “Any death ruled a homicide was included, regardless
of the method used. Assault related injuries that were not immediately
fatal were included if death followed within three months.” ( NEMJ
vol.329, no.15, pg. 1084). Right there, that raised a red flag in my
mind. If the case studies included deaths occurring three months after
an assault, one has to question the validity of those cases. The
questions that come to mind were; what were the cause of death for those
who were assaulted? Were the deaths related to the initial assault or
were they from other causes? These question were never answered in this
article or any other that Dr. Kellermann published in the New England
Journal of Medicine or other medical journals that he has written for.

The answer to the question is in the quotation from the paper. If the
death was not related to the initial assault, it would not have been
ruled a homicide.

David Friedman writes:

I have no strong opinion on the Kellerman study at this point, not
having made a sufficient effort to untangle the arguments by both sides.

That doesn’t seem to stop most people who post about it.

Incidently you can get the study (in pdf) and all of the data here

Most of the criticism of Kellermann’s study available on the web is of
truly dreadful quality.

The best available is by Gary Kleck:

Steve Kangas has written a reasonable summary of the contrary

But I think you are misreading the language you quote. There are two
sentences, each of which describes a sufficient condition for including
a death. The first is that it was ruled a homicide. That covers all
homicides, however long it takes the victim to die; the words are “any
death ruled a homicide.” The second is that assault related injuries are
included if death followed within three months. So those are cases that
were not ruled homicides.

You are mistaken. The first sentence gives the general rule, the
second clarifies the definition of homicide used. (That is, the death
had to occur within three months for it to be counted as a homicide.)
If you remain unconvinced, I suggest looking at the context of those
two sentences. The study is clearly about homicides, not “homicides
plus some other deaths”