Why was Moses able to go to Pharaoh and ask for his people to be let go when Moses was a murderer?

Moses had murdered a person in Egypt while he was living under the emperor Pharaoh. He ran and hid for 40 years to avoid being killed for killing someone. Then God had Moses go before Pharaoh and ask for the Jewish people to be let go. Remember he did miracles before Pharaoh like throwing his staff down and it turning into a snake. Why didn't Pharaoh have him arrested? I like Moses but I am curious.