Niagara Falls police are investigating four armed robberies in the city over the past four days. Three of the armed robberies were at convenience stores, while a fourth, just before midnight Thursday, involved a pizza delivery driver.

Niagara Falls police said the robberies are similar in some respects, but at this point they are unsure whether the cases are connected.

Niagara Falls Police Superintendent E. Bryan DalPorto, who began his job this week, said violent crime in the city is an issue he plans to address.

“We have had a rise in violent crime, but any rise has resulted in an increase in arrests. That’s a good thing – at least we know we are addressing the problem, but we’d like both numbers to go down.”

A store employee at a 7-Eleven in the 2600 block of Niagara Street told police that just after 3:30 a.m. Monday, two black men, both about 5 feet, 8 inches tall in hooded black winter coats and wearing ski masks, entered the store. One man pulled out a handgun and demanded that the clerk empty the register, taking approximately $100. The other man took cigarettes, lottery tickets and candy.

At 10:24 p.m. Tuesday, a man about 6 feet, 2 inches tall with a large build entered a 7-Eleven at 1504 Pine Ave. He appeared to be high on drugs, witnesses told police. The man went to the counter brandishing a steak knife and demanded that the clerk put all the money from the cash register into a plastic bag he was carrying. The man left with $40 and five packs of cigarettes. He was wearing a black leather jacket and black leather gloves, with a black checkered scarf covering most of his face.

In the third robbery, a man armed with a sword held up the 7-Eleven at 402 Niagara St. shortly before 3 a.m. Wednesday. He was described as a black male with an American flag bandanna covering his face wearing a black jacket.

In the fourth case, a driver for Sammy’s Pizza said he was delivering a pizza to an apartment building near 19th and Falls streets at 11:45 p.m. Wednesday when two men – both about 5 feet, 9 inches tall, with husky builds wearing black ski masks and dark clothing – confronted him with a machete. He said one demanded his wallet, threatening to kill him. He said he turned over his wallet containing $98 and Medicare and Social Security cards. The victim was able to drive away and call police, giving them the phone number of the person who called for the pizza delivery.

Anyone with information about any of the cases is asked to contact Niagara Falls police detectives at 286-4553.