Last One!

This is the modern day mystery. Sorry if it's kinda bloody.

Blood. Lots of it. New York PI Josh Weathers glanced around the scene. "Mr. Weathers, what have you gathered?" his assistant asked.
"One, don't call me that. Josh is fine. Second, the victim was subjected to some kind of lethal injection. There was a struggle, and the attacker somehow got the needle in him. I took a blood sample. Some on the ground from the cuts, and some from the body. Check and see if Chis Steel had any medical problems prior to the accident and what that poison is."
"Yes, sir."
The assistant was about to walk away when Josh said, "Don't call me that either."
The attendent looked embarrassed. "Y-yes, um, Josh."
Josh smirked at him. "That's better. Now get going!"
After the scans were done, Josh surveyed the results. "Low blood sugar, probably a diabetic." Josh muttered. "Wow, polonium. This attacker must have been serious." Polonium is a lethal poison that can kill rather quickly. One injection could easily kill hte fittest person. "How did he get it though? Only toxicologists have this, at least that's what I thought. There's been some smuggling going around."
"Mr. W...Josh, we have Chris's information." said his assistant. Josh sighed.
"Relax, Percy. Let me see those papers." Percy handed Josh the pages. As Josh read the pages searching for any politic or other enemies, Percy sat down. "The cops didn't find a lot of evidence evidence didn't they."
Percy shook his head no. "There was barely anything to look for. Besides, the evidence lead to a man in his early fifties. I'm pretty sure a fifty-three year old man could killed a twenty year old man. We're back to square one in suspects."
Josh nodded broodingly, scowling at the false leads. "I'm going back there tomorrow and saying if there are any evidence that the cops overlooked."
Percy quickly agreed. "Good idea. It never hurts to be careful. What did you learn from the scans?"
"Polonium. The killer somehow got his hands on polonium. I suspect there is some smuggling going on."
The next day, the two men trudged through the snow. When they near the crime scene, they quickly gathered as much information as possible before the falling snow could erase the evidence. Suddenly, a hand flew out of the shadows and grabbed Percy by the arm.
"Ahh!" he yelled jerking away. Josh whirled around. He karate kicked the masked attacker hard in the gut. The attacker turned to him, holding a needle in one hand and a dangerous looking dagger in the other. Percy now pulled out his gun and shot the man in the arm forcing him to drop the needle. Josh immediately kicked the needle into a snow drift and punched the man in the face. In pain and anger, the assailant lashed out with his dagger. Percy jumped in front of Josh, and the dagger struck home.
"Ugh," Percy groaned staggering backwards. Josh grabbed his own gun and shot the man in the back of the leg, then drove the flat part of the gun into the man's temple knocking him unconscious.
By now, the cops had arrived on the scene with an ambulance. "Get my assistant to a hospital, now!" Josh yelled at the people around him. Everyone jumped into action. Josh grabbed the needle from the snow. "Polonium."