The scriptures say, Moses wrote the law.<quoted text>
Pardon me to say, the "art of writing" was not so advanced in the time of Moses. MOST of his teachings were Oral (as for most prophets of the past). What was written down were ten commandments and some basic teachings.
Not the details about different sacrifices and details about Ark of YHWH!!
"And Moses wrote this law, and delivered it unto the priests the sons of Levi, which bare the ark of the covenant of the Lord, and unto all the elders of Israel."