GMP said it had spoken to officers at all 45 polling stations, none of whom received any reports, other than from Democracy Volunteers.
Out of the 45 polling stations, 41 said they did not have CCTV activated in the building as it would have compromised the secrecy of the vote during polling day, in line with official advice.
Of the CCTV reviewed, police said there was no evidence of anyone directing or coercing another regarding how to vote.
Volunteers were unable to provide descriptions of those allegedly involved, or timings – and no details were documented by observers.
“We have spoken to the four Democracy Volunteers observers present at polling stations on the day of the by-election – 26 February – who have shared with us their eyewitness account,” police said
“This includes some instances of more than one voter going into a booth at the same time, and instances of people looking over the shoulder of voters.
“The information they have provided to us estimates this may have happened on 32 occasions across 15 polling stations.
“The observers do not allege any verbal instruction or physical conduct that indicated one person was directing or coercing another regarding how to vote.”
“The absence of this information means there is no remaining reasonable line of enquiry,” police added.