Police spokesman, Emilian Kayima, told journalists in Kampala that Rogers Paul Mathias, 57, currently detained at Nalufenya, a high profile detention facility in Jinja District was found in illegal possession of government stores at his house in Bwebajja on Entebbe Road.
"We are investigating circumstances under which this American possessed the weapons supposed to be with Military officers. We are interrogating him to understand how he sneaked the deadly weapons into the country," Kayima said.
Mathias was arrested on Saturday in a police raid at his home after his wife, Lillian Keitesi reported a case of domestic violence.
Keitesi accused her husband of torturing her and being in possession of firearms and several other dangerous weapons.
Shortly after his arrest, Kampala Metropolitan Police commander, Commissioner Frank Mwesigwa said they searched at his home and found army uniforms, ammunitions and knives that are a reserve of armed forces.
Police say they are investigating the suspect on several offences including illegal possession of government stores.
In March last year, Immigration officers at Entebbe International Airport confiscated a rifle he had brought in the country illegally.
Police are also working with Immigration officers on another case against the suspect after he was found with expired passports.
Meanwhile,The head of the Internal Security Organisation (ISO), Col Frank Bagyenda Kaka, has dismissed as "trash" allegations that one of the two European men who died in two Kampala hotels last week had come to Uganda on his invitation.
It was reported yesterday that the two men died on February 5 and February 6 in Sheraton and Pearl of Africa hotels, that are about a kilometre apart.
The deceased are Tersvouri Toomajuha Petteri, 42, a Finland national, who died at Pearl of Africa Hotel on February 5, and Alex Sebastian, 41, a Sweden national, who died in his room at Sheraton Hotel on February 6.
Dr Moses Byaruhanga, the police surgeon, on Friday said postmortems could not immediately establish the causes of the deaths. He said they took samples from the bodies for further investigation.
Sources have said that when Petteri and a colleague arrived at the airport, they told security personnel that they were coming to Uganda to visit Col Bagyenda, which prompted one of the ISO operatives at the airport to call Col Bagyenda about his 'visitors'.
Col Bagyenda, the sources say, told the caller that he was not expecting any visitors from abroad, prompting security at the airport to detain and question the visitors.
As the questioning proceeded, the sources say, a one Apollo Kyabagye and two women identified as Faridah Nakaye and Carol Alinda and a policeman arrived at the airport to pick up the guests. On realising that the persons they had gone to pick up were undergoing questioning, sources say, the group escaped and only Alinda was arrested.
The guests, the sources add, were driven to Kampala for further questioning and Petteri proceeded to Pearl of Africa Hotel where he had been booked with his colleague, Suvi Linden, a politician in Finland, proceeding to another unnamed hotel.
Asked whether he had invited the deceased as alleged, Col Kaka said: "That is trash. For now I cannot give you details because we are still investigating. We don't do work through the media. It is unprofessional; it interferes with the investigations."
Intelligence sources suspect that Petteri could have been a victim of conmen, a line Col Bagyenda confirmed is of interest to ISO. He said the investigations are being jointly conducted by ISO and the police.
Kampala Metropolitan Police Commander Frank Mwesigwa said the people who gave Petteri a "forged" invitation were working with ISO operatives.
Police sources say the so-called ISO operatives who invited Petteri are the ones who referred him to Pearl of Africa Hotel for residence.
Petteri and his colleague allegedly presented an invitation letter at the airport indicating that Col Bagyenda had invited him to the country. Police sources say that Petteri owned a security company in Finland and perhaps intended to engage in similar business in Uganda, hence the need to engage with people charged with security.
"We are not taking these murders lightly because they involve foreigners and this might affect tourism and investment in the country," Col Bagyenda said.
Information regarding the death of Sebastian at Sheraton Hotel is still very scanty. Available information indicates that Sebastian, who was holding Swedish passport No 91056284, arrived in the country on February 5 and was booked into his room at 3am. He was discovered dead that morning after his wife's calls went unanswered and she alerted the hotel management who checked his room.
Swedish Ambassador Per Lindgarde said he was aware of the death of the Swedish national but that he had no details regarding the death.