I thought this move by LE was quite intriguing (in a smart way).
MOO: Some perps, perhaps this one, are very self-confident, cunning; think they can outsmart police. They may display a need to try to appear friendly and cooperative, might seek info on the direction of, or evidence in the case. They'll get further scrutiny.
Anyone known to police via other witness statements to have had an argument, but doesn't self-disclose, would get further scrutiny/questioned: "we heard ... why didn't you come forward...?"
Most people (not involved), who knew them well enough to have had an argument, wouldn't hesitate to get themselves eliminated as promptly as possible so they can concentrate resources on the real perps. But they may also have an added incentive to provide other information they may not have necessarily made an effort to otherwise. Meaning, they might not call in a tip if it seems insignificant or unimportant, but in person, when asked, "is there anything else, anything at all you can think of..." they may get the urge to tell more.