The weapon was found on an armed man who was killed by residents early Friday morning.
According to officers, the suspect was cornered by members of the public who claimed he had been terrorising the community.
By the time local administrators and police arrived, the man had already suffered fatal injuries.
A quick search at the scene led officers to recover a G3 rifle, two magazines, 68 rounds of 7.62x51mm ammunition, several blank cartridges, a penknife, and personal items believed to belong to the suspect.
Police later confirmed that the firearm had previously been reported missing in a case under investigation within Thika East.
In a brief statement, the National Police Service (NPS) said the recovered items were secured and would undergo forensic and ballistic analysis to determine whether the gun had been used in the string of robberies recently reported in the area.
Preliminary findings already suggest that the firearm may have changed hands multiple times, raising concerns about how widely illegal guns are circulating in Kiambu and neighbouring counties.
The NPS cautioned members of the public against taking the law into their own hands, noting that mob killings often interfere with investigations and deny victims a fair trial.
The police urged residents to report criminals through established channels instead of resorting to violence.
They emphasised that community cooperation plays a key role in ongoing security operations targeting illegal weapons.
The statement also highlighted the ongoing Operation Rudisha Bunduki (Bring Back the Gun), which encourages civilians to voluntarily surrender illegal firearms without fear of arrest.
Safety agencies, including the Kenya Defence Forces (KDF) and local administration units, are currently collaborating in intensified operations aimed at recovering stolen and unlicensed guns.
Authorities further encouraged the public to share information anonymously via toll-free hotlines or the DCI tip line, noting that even small details can help disrupt criminal networks.
As investigators piece together the movements of the recovered weapon, police say they are determined to trace its full history and identify all individuals connected to it.
The incident has revived public debate on rising insecurity and the growing number of illegal firearms in civilian hands, with police insisting they remain committed to restoring safety in affected communities.
