Why Is John 5:4 Missing From My Bible?

 (John 5:3b-4)"waiting for the moving of the water.  For an angel went down at a certain time into the pool and stirred up the water; then whoever stepped in first, after the stirring of the water, was made well of whatever disease he had." (NKJV) 

Many modern translations do not include the end of John 5:3 and all of John 5:4.  This verse is included in the KJV and the NKJV, while the LSB and NASB 1995 include it but put it in brackets.  Most translations such as the ESV, NIV, and CSB do not include it in the text, instead they have it in a footnote.  So what is going on here?  

The New Testament was originally written in Greek.  The KJV and NKJV use a Greek text known as the Textus Receptus (received text).  The Textus Receptus is mainly based on late Greek manuscripts and sometimes on the Latin Vulgate.  

On the other hand most modern translations are based on what is called the critical text.  It takes into account earlier Greek manuscripts which were not available to the King James translators in 1611.  

The earliest Greek manuscript to contain John 5:4 is Codex Alexandrinus (5th century).  The earlier Greek manuscripts do not include this verse.  They include P66 (around A.D. 175), P75 (around A.D. 200), Codex Sinaiticus (4th century), and Codex Vaticanus (4th century).  

It seems that John 5:4 may have been an explanatory note added by a scribe, that was later included in the text of the manuscripts by a copyist who mistakenly thought it belonged there.