This actually is important evidence the prosecution can use at trial, it is called CIRCUMSTANTIAL evidence.
The majority of the time a defendant is convicted on more than just one piece of evidence, they are convicted on the TOTALITY of the evidence presented.
Sure, a defendant can be convicted on just one piece of DIRECT evidence such as an eye witness who saw the defendant commit the murders, etc...But even in cases such as these there is often circumstantial evidence that goes along with it.
BK was indicted for killing 4 innocent college students who were suppose to be totally safe sleeping in their beds at four o'clock in the morning on 1122 King Road.
BK was living 10 miles away yet in the months leading up to the murders his phone was pinging on at least 12 different occasions on the same cell tower that the victim's used at their home on 1122 King Road. This is circumstantial evidence.
BK's phone pinged eleven times in the late evening and early morning hours as opposed to daytime hours when it would have been easier to spot him, again, this is also circumstantial evidence.
And yes, the defense will say that even though BK's phone pinged on the 1122 King Road cell tower, it still doesn't prove he was actually on King Rd, he could have been in the area doing other things as you say.
But.....the prosecution has this........
A white Hyundai Elantra was seen near the victims' home around the time of the killings. This is the exact type and color of car BK drives.
The car is another piece of circumstantial evidence to add to the cell tower circumstantial evidence to add to the circumstantial evidence of BK messaging a victim multiple times, to add to the circumstantial evidence of wearing medical gloves multiple times, to add to the circumstantial evidence of fitting a witnesses' description of a man in the house that night......
BK washing the car over and over, when it was dark BK put trash in the neighbor's trash bin, BK's crime questions on reddit, BK in college studying a serial killer who also killed 4 people at once, BK's online postings about mental health, possibly his history of negative interactions with women, and so forth......
And what might be considered direct evidence - BK's DNA on a knife sheath left next to a victim.
TOTALITY of evidence.